Allergy is a disease in which the immune system reacts abnormally to every day substances such as pollens, animal dander, mold spores, mites, certain foods and chemicals. All of these allergic reactions are unpleasant, some are serious, and a few can be fatal. The offensive substances causing allergies are known as allergens. An allergic reaction may be caused by inhaling or ingesting the allergen or may be the result of direct contact with the allergen.

What are the signs of allergy?

The most common signs are scratching, face rubbing and biting and chewing at the skin. Usual locations for signs of allergy are the flank, feet, face, particularly around the eyes, mouth and ears, as well as areas around the base of the tail. In dogs, allergies are often the underlying cause of persistent skin disease. However not all scratching is due to an allergy. Conditions such as thyroid disease, fleas and certain infections, such as ringworm, can cause similar
signs.

More..